Protein kinases regulate many different signaling processes by adding phosphate groups to proteins (Hunter, T., Cell 50 (1987) 823-829); particularly serine/threonine kinases phosphorylate proteins on the alcohol moiety of serine or threonine residues. The serine/threonine kinase family includes members that control cell growth, migration, differentiation, gene expression, muscle contraction, glucose metabolism, cellular protein synthesis, and regulation of the cell cycle.
Many diseases are associated with abnormal cellular responses triggered by protein kinase mediated events. These diseases include autoimmune diseases, inflammatory diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease or hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
The Aurora kinases are a family of serine/threonine kinases that are believed to play a key role in the protein phosphorylation events that are essential for the completion of essential mitotic events. The Aurora kinase family is made up of three key members: Aurora A, B and C (also known as Aurora-2, Aurora-1 and Aurora-3 respectively). Aurora-1 and Aurora-2 are described in U.S. Pat. No. 6,207,401 of Sugen and in related patents and patent applications, e.g. EP 0 868 519 and EP 1 051 500.
For Aurora A there is increasing evidence that it is a novel proto-oncogene. The Aurora A gene is amplified and the transcript/protein is highly expressed in a majority of human tumor cell lines and primary colorectal, breast and other tumors. It has been shown that Aurora A overexpression leads to genetic instability shown by amplified centrosomes and significant increase in aneuploidy and transforms Rat1 fibroblasts and mouse NIH3T3 cells in vitro. Aurora A-transformed NIH3T3 cells grow as tumors in nude mice (Bischoff, J. R., and Plowman, G. D., Trends Cell Biol. 9 (1999) 454-459; Giet, R., and Prigent, C., J. Cell Sci. 112 (1999) 3591-3601; Nigg, E. A., Nat. Rev. Mol. Cell Biol. 2 (2001) 21-32; Adams, R. R., et al., Trends Cell Biol. 11 (2001) 49-54). Moreover, amplification of Aurora A is associated with aneuploidy and aggressive clinical behavior (Sen, S., et al., J. Natl. Cancer Inst. 94 (2002) 1320-1329) and amplification of its locus correlates with poor prognosis for patients with node-negative breast cancer (Isola, J. J., et al., Am. J. Pathology 147 (1995) 905-911). For these reasons it is proposed that Aurora A overexpression contributes to cancer phenotype by being involved in chromosome segregation and mitotic checkpoint control.
Human tumor cell lines depleted of Aurora A transcripts arrest in mitosis. Accordingly, the specific inhibition of Aurora kinase by selective inhibitors is recognized to stop uncontrolled proliferation, re-establish mitotic checkpoint control and lead to apoptosis of tumor cells. In a xenograft model, an Aurora inhibitor therefore slows tumor growth and induces regression (Harrington, E. A., et al., Nat. Med. 10 (2004) 262-267).
Low molecular weight inhibitors for protein kinases are widely known in the state of the art. For Aurora inhibition such inhibitors are based on for example. quinazoline derivatives as disclosed in WO 00/44728; WO 00/47212; WO 01/21594; WO 01/21595; WO 01/21596; WO 01/21597; WO 01/77085; WO 01/55116; WO 95/19169; WO 95/23141; WO 97/42187; and WO 99/06396; pyrazole and triazole derivatives as disclosed in WO 02/22601; WO 02/22602; WO 02/22603; WO 02/22604; WO 02/22605; WO 02/22606; WO 02/22607; WO 02/22608; WO 02/50065; WO 02/50066; WO 02/057259; WO 02/059112; WO 02/059111; WO 02/062789; WO 02/066461; and WO 02/068415; pyrimidine derivatives as disclosed in WO 03/077921; WO 03/078423; WO 03/078426; WO 03/078427; and WO 04/000833; and imidazole, oxazole and thiazole derivatives as disclosed in WO 02/96905 and WO 04/005283.
WO 2005/002552 relates to pyrazole derivatives as inhibitors of cyclin dependent kinases (CDK), glycogen synthase kinase-3 (GSK-3) and Aurora kinase. WO 03/035065 relates to benzimidazole derivatives as kinase inhibitors, especially as inhibitors against kinase insert domain containing receptor (KDR) tyrosine kinase, spleen tyrosine kinase (SYK) and inducible T cell kinase (ITK). Some related tricyclic compounds are known as inhibitors of erythrocyte aggregation from U.S. Pat. Nos. 4,835,280A and 4,954,498A. Also Mertens, A., et al., J. Med. Chem. 30 (1987) 1279-1287; von der Saal, W., et al., J. Med. Chem. 32 (1989) 1481-1491; U.S. Pat. Nos. 4,666,923A; 4,695,567A and 4,863,945A describe related tricycles as erythrocyte aggregation inhibitors. U.S. Pat. No. 5,212,186A describes related tricycles for the treatment of cardiac insufficiency, hypertension and other diseases. WO 2005/111040 describes pyrrolobenzimidazolones with tubulin inhibitory activity as antiproliferative agents.